Flow control for powerline communications

ABSTRACT

A method of powerline communications in a powerline communications (PLC) network including a first node and at least a second node. The first node transmits a data frame to the second node over a PLC channel. The second node has a data buffer for storing received information. The second node runs a flow control algorithm which determines a current congestion condition or a projected congestion condition of the data buffer based on at least one congestion parameter. The current congestion condition and projected congestion condition include nearly congested and fully congested. When the current or projected congestion condition is either nearly congested or fully congested, the second node transmits a BUSY including frame over the PLC channel to at least the first node. The first node defers transmitting of any frames to the second node for a congestion clearing wait time.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 14/540,111, filed on Nov. 13, 2014, which is acontinuation of and claims the benefit of U.S. patent application Ser.No. 13/529,146, filed on Jun. 21, 2012, now U.S. Pat. No. 8,913,495issued on Dec. 16, 2014, which claims the benefit of ProvisionalApplication Nos. 61/499,555, 61/499,418 and 61/499,357, all of whichwere filed on Jun. 21, 2011, all applications are herein incorporated byreference in their entireties.

FIELD

Disclosed embodiments relate generally to the field of powerlinecommunications, more particularly to flow control in powerlinecommunication networks.

BACKGROUND

Powerline communications (PLC) include systems for communicating dataover the same medium (i.e., a wire or conductor) that is also used totransmit electric power to residences, buildings, and other premises.Once deployed, PLC systems may enable a wide array of applications,including, for example, automatic meter reading and load control (i.e.,utility-type applications), automotive uses (e.g., charging electriccars), home automation (e.g., controlling appliances, lights, etc.),and/or computer networking (e.g., Internet access), to name only a few.

A PLC network includes a plurality of nodes, generally including a base(or concentrator) node and a plurality of service nodes (includingswitch nodes and terminal nodes) configured in a tree-likeconfiguration. During network operation, some nodes in the PLC networkmay witness a high rate of incoming frames causing the conventionalsingle data buffer which provides memory for both transmission data andreception data, or their receive buffer for separate transmission bufferand reception buffer embodiments, to become full. Once the data bufferfor receiving data is full, the communication device at the node willnot be able to receive any incoming frames sent from other networknodes, which will result in dropped frame(s), as well as theretransmission of the dropped frames by the sender node(s). A known dataflow control (hereafter “flow control”) mechanism used in conventionalPLC networks involves having the sender node device defer itstransmissions for a fixed period of time after the sender node receivesan indication from the receiving node that the receive node's databuffer is full.

SUMMARY

One embodiment comprises a method of powerline communications in apowerline communications (PLC) network including a first node and atleast a second node. The first node transmits a data frame to the secondnode over a PLC channel. The second node has a data buffer for storingreceived information. The second node runs a disclosed flow controlalgorithm which determines a current congestion condition or a projectedcongestion condition of the data buffer for receiving data based on atleast one congestion parameter.

The current congestion condition and projected congestion conditioninclude uncongested, nearly congested, and fully congested levels. Whenthe current or projected congestion condition is either nearly congestedor fully congested, the second node transmits a BUSY comprising frameover the PLC channel to at least the first node. Responsive to the BUSYcomprising frame, the first node defers transmitting any frames to thesecond node for a congestion clearing (i.e. reducing) wait time. In oneembodiment the BUSY comprising frame includes the congestion clearingwait time. Other disclosed embodiments include modems and communicationdevices implementing disclosed flow control algorithms.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to the accompanying drawings, which are notnecessarily drawn to scale, wherein:

FIG. 1 shows a depiction of the workings of a disclosed flow controlalgorithm, according to an example embodiment.

FIG. 2 shows a depiction of the workings of a disclosed flow controlalgorithm, according to another example embodiment.

FIG. 3 is a block diagram schematic of a communication device having adisclosed modem that implements powerline communications using adisclosed flow control algorithm, according to an example embodiment.

FIG. 4 is a flowchart for a method of powerline communications in a PLCnetwork including a first node and at least a second node having a databuffer for storing received information that runs a disclosed flowcontrol algorithm, according to an example embodiment.

DETAILED DESCRIPTION

Disclosed embodiments now will be described more fully hereinafter withreference to the accompanying drawings. Such embodiments may, however,be embodied in many different forms and should not be construed aslimited to the embodiments set forth herein. Rather, these embodimentsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of this disclosure to those having ordinaryskill in the art. One having ordinary skill in the art may be able touse the various disclosed embodiments and there equivalents. As usedherein, the term “couple” or “couples” is intended to mean either anindirect or direct electrical connection, unless qualified as in“communicably coupled” which includes wireless connections. Thus, if afirst device couples to a second device, that connection may be througha direct electrical connection, or through an indirect electricalconnection via other devices and connections.

In a first embodiment flow control algorithms are disclosed whichdynamically sense the current congestion condition (e.g., level) of thedata buffer for receiving data at the node to support the node whenacting as a destination (receiving) node, and can also optionallydetermine the projected congestion level given the node's currentcongesting level and the node's scheduled net frame flux. If the currentcongestion level or projected congestion condition is at least at apredetermined nearly congested level (e.g, 80% or 90% full), thedestination node can send a signal to the sender node(s) which delaystheir subsequent data frame transmissions to the destination node for acongestion clearing (i.e. reducing) wait time. A data buffer fillinglevel below the nearly congested level can be considered uncongested.

Delayed frame transmissions proactively limit the destination node fromexperiencing incoming frame rates sufficient to cause its data buffer tobecome fully congested (i.e. 100% full) to avoid the loss of data,through use of a disclosed BUSY comprising frame including on oneembodiment a BUSY-ACCEPT frame when at a nearly congested level, and aBUSY-REJECT frame when at a fully congested level. By reducing framedrops, disclosed flow control algorithms also reduce retransmission ofdropped frames. Disclosed flow control algorithms can be used at base(or concentrator) nodes in the PLC network, or at service nodesincluding switch nodes and terminal nodes.

A node acting as a destination node in the PLC network can accept anincoming frame from a transmitting (sender) node if the destinationnode's data buffer for receiving data is not full, and can check whetherthe receive node's data buffer for receiving data is nearly congestedbased on the final data buffer size. The final data buffer size as usedherein refers to a measure of the filling level of the data buffer forreceiving data after storing the scheduled received data frame(s), andthus defines the remaining storage capacity of the data buffer. Adisclosed flow control algorithm determines the current congestioncondition and optionally the projected congestion condition (whichconsiders the scheduled data frames to be received) based on one or morecongestion parameters.

The congestion parameters can include the final data buffer size, and ascheduled net frame rate flux that considers the rate of scheduledoutgoing frames from the node which frees buffer space if a single databuffer is used for transmission and reception data compared to thescheduled rate of incoming frames to the node. The destination node canobtain an estimate of the rate of incoming frames based on the weightedaverage of the incoming rate of past frames.

Regarding the final data buffer size, when the incoming frame(s)increases the final data buffer size beyond a predetermined threshold(e.g., the data buffer is ≧90% full) after receipt of the scheduled dataframe(s), a nearly congested condition can be deemed to be present. Thescheduled net frame rate flux can be a binary parameter, based onwhether the scheduled arrival rate of frames >K*scheduled outgoing framerate, where K can be chosen to be anywhere from 0 to less than 1. Thescheduled net frame rate flux selected can be indicative of the flowcontrol being active during which time the wait time is indicated to thetransmitting node(s) to slow its frame transmission rate to the nodehaving disclosed flow control assistance. During the time of flowcontrol, the K value can be reduced from a value >1 (before flowcontrol) to a value between 0 and 1 (during disclosed flow control).

As shown in the depiction of FIG. 1, if the flow control algorithm atthe destination node 110 determines the destination node's data bufferfor receiving data 111 is nearly congested, but not fully congested, thedestination node 110 can proactively (i.e. before full congestion) senda BUSY-ACCEPT frame 125 to the sender node 120. The BUSY-ACCEPT frame125 indicates to the sender node 120 that the destination node 110 hasaccepted the frame, but its data buffer 111 is nearly congested. If thereceived data frame 115 is received by the destination node 110 whileits data buffer 111 is fully congested, the data frame will be droppedand a BUSY-REJECT frame 135 will be sent by the destination node 110 tothe sender node 120.

The BUSY-ACCEPT frame 125 and BUSY-REJECT frame 135 can both comprisemodified conventional acknowledgement (ACK) frames (i.e. an ACK framehaving a preamble, and a PHY header), and can follow the same channelaccess procedure as far an ACK frame, where the ACK is transmitted aftera Reduced Interframe Space (RIFS) duration following the reception of aframe by the intended receiver. There is generally no Carrier SenseMultiple Access (CSMA)/Collision Avoidance (CA) performed. DisclosedBUSY-ACCEPT 125 and BUSY-REJECT frames 135 can be created using aspecial Delimiter Type (DT) in one of the ACK PHY header fields. The DTfield can provide added information of the PHY frame being transmitted,including whether it is a DATA frame expecting ACK/NACK, ACK or NACKframe, and whether it is a BUSY-REJECT frame or BUSY-ACCEPT frame.

Upon reception of a BUSY-ACCEPT frame 125 or BUSY-REJECT frame 135, thesender node 120 can defer its frame transmissions to the destinationnode 110 until a congestion clearing wait time. The value of thecongestion clearing wait time can be selected to be either a fixed(constant) system specific parameter, or can determined as a dynamicparameter using a dynamic algorithm, such as disclosed in the thirdembodiment described below.

In a second embodiment, a flow control algorithm includes a neighboringnode alert mechanism which helps avoid the destination node's databuffer for receiving data 111 from becoming fully congested, includingsignaling that stops otherwise sender nodes in the neighborhood framesfrom sending frame(s) to the destination node no when the destinationnode's data buffer for receiving data is nearly or fully congested. Thedestination node 110 uses a disclosed flow control algorithm todynamically sense the current congestion level of its data buffer 111,including whether the data buffer 111 is nearly congested or fullycongested, as opposed to being uncongested.

FIG. 2 shows a depiction of the workings of a disclosed flow controlalgorithm, according to another example embodiment. When the destinationnode 110 receives the data frame 115 from the sender node 120, thedestination node 110 can accept the data frame 115 if its data bufferfor receiving data 111 is not fully congested, including when it isnearly congested, and drop the data frame 115 if it is fully congested.When a sender node 120 sends a data frame 115 to a destination node 110in the case destination node's data buffer 111 is nearly congested orfully congested, the destination node 110 in this embodiment can send aBUSY comprising frame 125/135 after a contention interframe spacing(CIFS) time shown in FIG. 2 as “aCIFS” as it is referred to in the IEEEP1901.2 standard.

The neighborhood nodes shown as Node A 220, Node B 225 and Node C 230also receive the BUSY comprising frame 125/135 (which can be aBUSY-ACCEPT frame 125 or BUSY-REJECT frame 135) along with the sendernode. Responsive to the BUSY comprising frame 125/135, the neighborhoodnodes, comprising Node A 220, Node B 225 and Node C 230, and the sendernode 120, all defer their transmissions to the destination node 110 fora time period equal to the congestion clearing wait time. As describedabove, the BUSY comprising frame 125/135 can comprise a modified ACKframe and the channel access mechanism can be the mechanism used by astandard ACK frame.

Although disclosed BUSY comprising frames can be similar to standard ACKframes, one distinction is that disclosed BUSY comprising frames includeinformation so that any node in the neighborhood of the destination nodethat receives the BUSY comprising frame can identify the destinationnode sending the BUSY comprising frame, such as based on information inthe DT field as described above relative to the first embodiment.Responsive to the BUSY comprising frame the neighborhood nodes can detertheir transmissions to the destination node for a time period equal tothe congestion clearing wait time.

Since all nodes in the neighborhood of the destination node defer theirtransmissions to the destination node, if the destination node transmitsduring the congestion clearing wait time, such transmission(s) willclear memory space in its data buffer 111 (for the typical case of asingle data buffer for both receive and transmit data), thus reducingthe congestion level. As with the first embodiment, the value of thecongestion clearing wait time may be system specific and constant, orcan be determined dynamically based on the network conditions. Thisembodiment also helps to avoid wastage of PLC network resources thatwould have occurred when network nodes send their frames to a congestednode when using known flow control methods.

Although a node may send a BUSY comprising frame, it cannot beguaranteed that every node in its neighborhood will successfully receivethe BUSY comprising frame, as there may be a loss of BUSY comprisingframe information, such as due to node collisions or frame error. Insome embodiments, particularly environments prone to frame loss, thedestination node when in the nearly congested or fully congested statecan use the conventional ACK channel access procedure to transmit itsnext frame.

The following example options may be used by the destination node whenin the nearly congested or fully congested condition to transmit itsnext data frame:

-   1. The destination node transmits the data frame immediately    following its transmission of a BUSY comprising frame, separated    only by an interframe space (IFS), shown in FIG. 2 as aCIFS.-   2. The destination node can transmit the data frame, instead of an    ACK or BUSY comprising frame, using the channel access mechanism of    the ACK after receiving a frame while being in the fully congested    state. The sender node will recognize the loss of the transmitted    frame by the lack of the ACK frame from the destination node in    response, and the destination node will be able to obtain    contention-free access to the PLC channel to transmit frames to    reduce congestion (for single data buffer embodiments).-   3. The destination node can transmit its next data frame, instead of    ACK or BUSY comprising frame, using the channel access mechanism of    the ACK after receiving a frame while in the nearly congested or    fully congested state. The sender can recognize whether their    transmitted frame was received or not, by using a special field in a    header of the frame (e.g., one of the DT reserved fields in the PHY    header) sent by the destination node that indicates the    success/failure of the sender node's earlier attempt to send a frame    to the destination node. The sender node will not process the rest    of the data frame if it was not sent to (addressed to) it. The    destination node will then be able to obtain contention free access    to the PLC channel to transmit frames to reduce congestion.

In a third embodiment, a flow control algorithm provides a dynamicmethod to determine the amount of congestion clearing wait time that thesender node(s) defers transmissions to a destination node based thecurrent congestion level at the destination node together with theperceived network load referred to above as the net scheduled frame rateflux. For example, an estimate of the rate of incoming frames can bebased on the weighted average of the incoming rate of past frames.

In PLC networks, a network wide Extended Inter frame Space (EIFS) isused to account for one single packet transmission time, where if thepreviously received frame contains an error, then the node defers for anEIFS duration before transmitting a frame. The congestion clearing waittime can be set to K*EIFS, where K is a constant. K is shown as aninteger below based on IEEE P1901.2, but can also be a fraction forother or future PLC standards. The value of K can be specified in theBUSY comprising frame 125/135 sent by the destination node as describedabove for use to indicate that the data buffer at the destination nodeis at least nearly congested. In PLC standards such as IEEE P1901.2networks, the PHY header is referred to as a frame control header (FCH),and the two bits [0 and 1] in the 8^(th) byte field of the FCH(Currently reserved) can be used to represent the value of K to allowthe sender node(s) upon receipt of the BUSY comprising frame from thedestination node to compute the congestion clearing wait time. Anexample set of K values obtained from a 2 bit pattern is shown in theTable below.

Bit Pattern K 00 1 01 2 10 3 11 4

Higher K values can be used when the perceived network load for thedestination node is higher, while lower K values can be used when theperceived network load (e.g. scheduled net frame flux) for thedestination node is lower. This embodiment allows a receiving node todynamically determine the congestion clearing wait time period based onits perceived traffic load, and transmit the dynamically determinedcongestion clearing wait time to other nodes in the PLC network. It isnoted that more granularity in the choice of K can be obtained if morethan 2 bits are allocated in the PHY header (e.g., FCH in IEEE P1901.2networks) to represent the K value.

FIG. 3 is a block diagram schematic of a communication device 300 havinga disclosed modem 304 that implements powerline communications using adisclosed flow control algorithm, according to an example embodiment.Communication device 300 can be used at base (or concentrator) nodes inthe PLC network, or at service nodes including switch nodes and terminalnodes.

Modem 304 includes a processor (e.g., a digital signal processor, (DSP))304 a coupled to an associated memory 305 that that stores a disclosedflow control algorithm that may include any combination of the first,second and third embodiments described above, including the first,second and third embodiments in one particular embodiment, whichprovides code for the flow control algorithm. Memory 305 comprisesmachine readable storage, for example, static random-access memory(SRAM).

In operation, the processor 304 a is programmed to implement the flowcontrol algorithm. Communications device 300 is also shown including adata buffer 111 (which provides storage for both transmit data andreceived data) coupled to the processor 304 a for storing receivedinformation from other nodes in the PLC network via PLC transceiver(TX/RX) 306. Although not shown, communications device 300 can includeboth a receive buffer and a reception buffer. Moreover, although shownas separate blocks, memory 305 and data buffer 111 may be provided by asingle memory device having a partitionable memory. Modem 304 includes atimer 307, such as for ACK transmission, CSMA/CA back-off and datatransmission purposes.

The PLC transceiver (TX/RX) 306 is communicably coupled to the modern304 for coupling of the communications device 300 to the sharedpowerline 340. Transceiver 306 facilitates communications with other SNsand the BN on the powerline 340.

When the current or projected congestion condition is either nearlycongested or fully congested, the modem 304 generally sends at least atrigger command to the PLC transceiver 306 to transmit a BUSY comprisingframe over the powerline 340 (that provides a PLC channel) to at leastone sender node in its neighborhood which is operable for the sendernode to defer transmitting of any frames to the communications device300 for a congestion clearing wait time.

The modem 304 is shown formed on an integrated circuit (IC) 320comprising a substrate 325 having a semiconductor surface 326, such as asilicon surface. Memory 305 may be included on the IC 320. In anotherembodiment the modem 304 is implemented using 2 processor chips, such as2 DSP chips. Besides the DSP noted above, the processor 304 a cancomprise a desktop computer, laptop computer, cellular phone, smartphone, or an application specific integrated circuit (ASIC).

Disclosed modems 304 and disclosed communications devices 300 can beused in a PLC network to provide a networked device that in service isconnected to a powerline via a power cord. In general, the “networkeddevice” can be any equipment that is capable of transmitting and/orreceiving information over a powerline. Examples of different types ofnetworked devices include, but are not limited or restricted to acomputer, a router, an access point (AP), a wireless meter, a networkedappliance, an adapter, or any device supporting connectivity to a wiredor wireless network.

FIG. 4 is a flowchart for an example method 400 of powerlinecommunications in a PLC network including a first node and at least asecond node having a data buffer for storing received information thatruns a disclosed flow control algorithm, according to an exampleembodiment. In step 401, the first node transmits a data frame to thesecond node over a PLC channel.

In step 402 the flow control algorithm determines a current congestioncondition or a projected congestion condition of its data buffer basedon at least one congestion parameter. The current congestion conditionand projected congestion condition include nearly congested, fullycongested, and uncongested. In step 403, when the current projectedcongestion condition or projected congestion condition is either nearlycongested or fully congested, the second node transmits a BUSYcomprising frame over the PLC channel to at least the first node. Asdescribed above, the BUSY comprising frame can be a BUSY-ACCEPT frame125 or a BUSY-REJECT frame 135. The BUSY comprising frame can includethe congestion clearing wait time. Step 404 comprises the first nodedeferring transmitting of any frames to the second node for a congestionclearing wait time.

The congestion parameter can comprise a final data buffer size, and forconventional single data buffer embodiments a scheduled net frame rateflux parameter that considers a scheduled rate of outgoing frames fromthe second node compared to a scheduled rate of incoming frames to thesecond node. In one embodiment, if the flow control algorithm determinesthe current congestion condition or projected congestion condition isnearly congested, the second node accepts the data frame and the BUSYcomprising frame comprises a BUSY-ACCEPT frame, and if the flow controlalgorithm determines the current congestion condition current is fullycongested, the second node drops the data frame and the BUSY comprisingframe comprises a BUSY-REJECT frame. The BUSY-ACCEPT frame andBUSY-REJECT frame can both be transmitted using a modified ACK framehaving a field in a PHY header portion which includes information whichdistinguishes the modified ACK frame from a standard ACK frame, such asa DT field in a PHY header portion of the modified ACK frame asdescribed above. The scheduled net frame rate flux parameter cancomprise determining if the scheduled rate of incoming frames >K·thescheduled rate of outgoing frames, where 0<K<1.

As described above, the scheduled net frame rate flux selected can beindicative of the flow control being active during which time thecongestion clearing wait time is indicated to the transmitting node(s)to slow its frame transmission rate to the node having disclosed flowcontrol assistance. During the time of flow control, the K value canreduce from a value >1 (before disclosed flow control) to a valuebetween 0 and 1 (during disclosed flow control).

In one embodiment the PLC network further comprises at least node A,wherein node A, the first node and second node are in a commonneighborhood, and node A also receives the BUSY comprising frame anddefers transmitting any frames to the second node for the congestionclearing wait time. In this embodiment, when the current congestioncondition or projected congestion condition is either nearly congestedor fully congested, and the destination node transmits its next dataframe after the BUSY comprising frame either:

(i) following its transmission of the BUSY comprising frame after aninterframe space (IFS), or

(ii) as a modified ACK frame using a channel access mechanism for astandard ACK frame, where the next data frame has a field in a headerportion (e.g., a DT field in a PHY header) that includes informationwhich distinguishes the modified ACK frame from the standard ACK frame,or

iii) as a modified ACK frame using the channel access mechanism for thestandard ACK frame, where the next data frame has a first field in aheader portion which includes information which distinguishes themodified ACK frame from the standard ACK frame and a second field insaid header portion which indicates a success or failure of the firstnode's transmission of the data frame.

The second node can dynamically determines the congestion clearing waittime as a congestion clearing wait time variable including at least ahigher value and a lower value. The higher value can be used when thescheduled net frame rate flux parameter is at a higher net frame rateflux, and the lower value used when the scheduled net frame rate fluxparameter is at a lower net frame rate flux. The congestion clearingwait time can be set to set to K* an EIFS used in the PLC network, whereK is selected from a set of constants and is specified in a field of aheader portion of the BUSY comprising frame.

Many modifications and other embodiments of the invention will come tomind to one skilled in the art to which this Disclosure pertains havingthe benefit of the teachings presented in the foregoing descriptions,and the associated drawings. Therefore, it is to be understood thatembodiments of the invention are not to be limited to the specificembodiments disclosed. Although specific terms are employed herein, theyare used in a generic and descriptive sense only and not for purposes oflimitation.

We claim:
 1. A powerline communications (PLC) network comprising: a PLCchannel; and a first node coupled to said PLC channel; said first nodeconfigured to receive an ACK frame that includes a delimiter type field;and wherein said first node defers transmission of a data frame oversaid PLC channel for a congestion clearing wait time upon receivingeither a BUSY-ACCEPT or a BUSY-REJECT delimiter type field.
 2. The PLCnetwork of claim 1 wherein said first node is a base node.
 3. The PLCnetwork of claim 1 wherein said first node is a service node.
 4. The PLCnetwork of claim 3 wherein said first node is a terminal node.
 5. ThePLC network of claim 1 wherein the first node is located within a modem,a computer, a router, an access point, a wireless meter, a networkedappliance, or an adapter.
 6. The PLC network of claim 1 furthercomprising a neighborhood node coupled to said PLC channel; saidneighborhood node also defers transmission of a data frame over said PLCchannel for a congestion clearing wait time upon receiving either saidBUSY-ACCEPT or said BUSY-REJECT delimiter type field.
 7. A powerlinecommunications (PLC) network comprising: a PLC channel; and a secondnode having a data buffer coupled to said PLC channel, said second nodeconfigured to transmit an ACK frame over said PLC channel, said ACKframe includes a delimiter type field; wherein said delimiter type fieldis BUSY-REJECT if said data buffer is full, and said delimiter typefield is BUSY-ACCEPT if said data buffer is not full but is beyond athreshold.
 8. The PLC network of claim 7 wherein said delimiter typefield is ACK when said data buffer is not beyond said threshold.
 9. ThePLC network of claim 7 wherein said delimiter type field is NACK whensaid data buffer is not beyond said threshold.
 10. The PLC network ofclaim 7 wherein said second node is a base node.
 11. The PLC network ofclaim 7 wherein said second node is a service node.
 12. The PLC networkof claim 11 wherein said second node is a terminal node.
 13. The PLCnetwork of claim 7 wherein the second node is located within a modem, acomputer, a router, an access point, a wireless meter, a networkedappliance, or an adapter.
 14. A communication device comprising: apowerline that provides that provides a powerline communications (PLC)channel; a PLC transceiver coupled to said PLC channel; and anintegrated circuit (IC) coupled to said PLC transceiver; said ICincluding a modem having a processor; said IC also including a databuffer coupled to said processor; wherein said modem is configured tosend a trigger command to said PLC transceiver to transmit an ACK frameover said PLC channel, said ACK frame includes a delimiter type field;further wherein said delimiter type field is BUSY-REJECT if said databuffer is full, and said delimiter type field is BUSY-ACCEPT if saiddata buffer is not full but is beyond a threshold.
 15. The communicationdevice of claim 14 wherein said modem is a base node.
 16. The PLCnetwork of claim 14 wherein said modem is a service node.
 17. The PLCnetwork of claim 16 wherein said modem is a terminal node.